1. Field of the Invention
The present invention relates to data transmission in a wireless communication system. More particularly, the present invention relates to technologies for transmitting data from a base station to a mobile station in a wireless communication system using a multiple hop relay scheme.
2. Description of the Related Art
With advances in technologies from 1st generation mobile systems to 3rd or future generation communication systems, studies related to efficient operations and improved throughput of the system have been performed to realize high-speed transmission and satisfaction of user demand. The studies for efficient operations and improved throughput of the system included a multi-hop transmission scheme, which is an extension beyond a conventional single-hop transmission scheme which only a direct transmission from a Base Station (BS) to a Mobile Station (MS) is allowed. In a system supporting a multi-hop relay scheme, a signal can be transmitted from a BS to a MS via a Relay Station (RS), or directly transmitted to the MS. The system supporting the single-hop transmission scheme has a structure in which a BS exists in each cell, and directly connects to an MS without one or more repeaters (i.e. RSs.)
On the other hand, the system supporting the multi-hop transmission scheme has a structure in which one or more RSs are arranged in each cell between the BS and the MS. The RS repeats a signal from the BS to the MS so as to improve reception signal performance of the MS particularly in a cell boundary area or a shadow area. In other words, by using the RS, MSs in the shadow area can successfully receive signals from the BS. The shadow area comprises an area where communication between the BS and the MS is almost impossible. In the latter multi-hop system, a single cell may be comprised of one BS, one or more RSs, and one or more MSs. Using the one or more RSs in one cell has an advantage to over the drawbacks of installing an additional BS in the cell. For example, the RS can be installed less expensively than installing the BS. The RS generally transmits signals from a BS to an MS by merely amplifying signals received from the BS and by transmitting the signals to the MS or another RS, or by transmitting signals to the MS or another RS after decoding signals received from the BS, detecting errors in the signals, and then re-encoding the signals at the RS.
In the meanwhile, a signal from the RS can be received by an unintentional destination, e.g. an MS or another RS, because RSs are installed so as to keep a distance long enough to prevent an interference noise from occurring. In such a case, the signal received at the unintentional destination can make a noise in communication, which results in deteriorating overall throughput of the system. Such a case is below explained with reference to FIG. 1.
FIG. 1 illustrates data transmission in a conventional wireless communication system. Referring now to FIG. 1, a first frame 101, a second frame 102, a third frame 103, and a fourth frame 104 each indicate a time interval in which a BS, at least one RS, and at least one MS, transmit and receive data. In the frames 101 to 104, Node 0 (N0) 111, 121, 131 and 141 indicates a BS; Node 1 (N1) 113, 123, 133 and 143, Node 2 (N2) 115, 125, 135 and 145, Node 3 (N3) 117, 127, 137 and 147, and Node 4 (N4) 119, 129, 139 and 149 each indicate an RS; and Node 5 (N5) 120, 130, 140 and 150 indicates an MS. In the first frame 101, N0 111, N2 115 and N4 119 become transmitters, and N1 113, N3 117 and N5 120 become receivers.
In the first frame 101, the transmitters simultaneously transmit data to the receivers, that is, N0 111, N2 115 and N4 119 simultaneously transmit data to N1 113, N3 117 and N5 120, respectively.
In the second frame 102, conversely, N1 123, N3 127 and N5 130 become transmitters, and N0 121, N2 125, and N4 129 become receivers, and N1 123, N3 127 and N5 130 simultaneously transmit data to N0 121, N2 125, and N4 129, respectively.
In the third frame 103, in order to forward data received at the first frame 101, N1 133 and N3 137 become transmitters, and N2 135 and N4 139 become receivers. In the third frame 103, N1 133 and N3 137 simultaneously transmit data to N2 135 and N4 139, respectively.
In the fourth frame 104, in order to forward data received at the second frame 102, N2 145 and N4 149 become transmitters and N1 143 and N3 147 become receivers. In the fourth frame 104, N2 145 and N4 149 simultaneously transmit data to N1 143 and N3 147, respectively. However, the aforementioned transmission can cause noises in receiving data at each node, which is described below in detail referring to FIG. 2.
FIG. 2 illustrates an example of causing noises at the first frame 101 by transmission of neighboring nodes. Referring now to FIG. 2, it is assumed that at the first frame 101, N0 111 and N2 115 transmit data to N1 113 and N3 117, respectively, and N1 113 and N3 117 receive data from N0 111 and N2 115, respectively. It is also assumed that Range 210 is an area where data transmitted from N0 111 reaches, and Range 220 is an area where data transmitted from N2 115 reaches. When N0 111 and N2 115 simultaneously transmit data to N1 113 and N3 117, respectively, at a predetermined time interval, the receiver N1 113 is located within an overlapped region 230 of Ranges 210 and 220. N1 113 receives data from N2 115 as well as N0 111. Accordingly, data from N2 115 intended for N3 117 may cause noise in communication between N0 111 and N1 113. As stated above, data transmission of neighboring nodes, especially of RSs, may cause noises because of their geographic proximity, resulting in deteriorating overall throughput of the wireless communication system. Therefore there is a need for transmitting data while reducing interference noise at nodes such as a BS and an RS.